Peroxide-dipersulfate bleaching of cotton fibers



United States Patent 6 3,026,166 PEROXIDE-DIPERS UTJFATE BLEACHING F CQTTGN FIPsERS Gerald Thomas Gaiiagher, Snyder, and Norbert Weinberg, Bufialo, I -LY assignors to Fit (1 Corporation, a corporation of Delaware No Drawing. Filed. Oct. 9, 1%9, Ser. No. 345,310 6 Claims. (\Cl. 8-111) This invention relates to the bleaching of cotton fibers, and more particularly to an improvement in the method of cold-bleaching cotton fibers with aqueous hydrogen peroxide solutions.

It has been known for many years that cotton fibers can be bleached with aqueous hydrogen peroxide solutions at normal room temperatures. In this method, which is described generally in US. Patent 2,107,297, and referred to in the art as cold-bleaching, the fibers are dampened with the bleach liquor by being immersed in a hydrogen peroxide bleach bath, and thereafter squeezed free of excess solution to the point of dampness, or saturation. The dampened fibers then are permitted to stand at room temperature for several hours. Fibers treated in accordance with this simple method, which has minimal capital and equipment requirements, exhibit considerably improved brightnesses, and otherwise generally have desirable properties.

Cold-bleached cotton fibers suffer one major disadvantage, however. Their absorbencies, that is their abilities to be wetted with water, are poor. This means that they are not readily receptive to many post-bleaching treatments; as an example, they are difiicult to dye.

This poor absorbency of cold-bleached cotton fibers is not shared by cotton fibers bleached by hydrogen peroxide solutions at elevated temperatures, for example in a steam atmosphere. For this reason, steam-bleaching has supplanted cold-bleaching in many applications where good absorbency is a requirement. This is despite the desirability from an operational point of view, of applying the coldbleaching method to small lot and special bleaching, where its small capital and equipment requirements are a decided advantage.

By reason of the advantages of the cold-bleaching method, it has long been desired to provide such a method which would operate to provide bleached cotton fibers having the general good properties of cold-bleached fibers, but at the same time having satisfactory absorbencies.

It is a feature of this invention to provide a coldbleaching method for the bleaching of cotton fibers with hydrogen peroxide solutions, which operates to provide fibers having high brightnesses and high absorbencies.

It is a further feature to provide such a method which operates to provide fibers having these desirable characteristics, without damaging the fibers or otherwise rendering them unsuitable for use.

It is yet a further feature to provide such a method which is economical to operate, not requiring an increase in the total active oxygen content of the bleach solution, and not introducing harmful agents into the operation.

It has nowbeen found, quite surprisingly, that if a small amount of a dispersulfate of an alkali metal or ammonium is added to a typical hydrogen peroxide coldbleach formulation, and the resulting solution employed in the bleaching of cotton fibers by conventional coldbleaching techniques, the bleached fibers resulting from the treatment have greatly improved absorbencies. The dipersulfate is used to replace a portion of the hydrogen peroxide in the solution, and therefore does not increase the total active oxygen requirements of the solution. The improvement in absorbencies is such that fibers bleached in accordance with the present method, and with the present solutions, absorb water in as little as about one thir- BfiZfiJfih' Patented Mar. 2%, 1962 tieth of the time required by similar fibers bleached with hydrogen peroxide solutions not containing the dipersulfate. Furthermore, the bleached fibers of the present invention exhibit this improved absorbency without any sacrifice in the other desirable properties of cold-bleached fibers. For example, the bleached fibers of the present invention do not undergo undue degradation, and they do not contain undue amounts of harmful impurities. It has even been found that they exhibit somewhat improved brightnesses when compared with fibers bleached by the same technique, with a hydrogen peroxide bleaching solution not containing the dipersulfate.

These ends are accomplished in accordance with the method of the present invention, by dampening the cotton fibers with an aqueous alkaline hydrogen peroxide solution containing as an essential ingredient an alkali metal dipersulfate or ammonium dipersulfate, maintaining the fibers in dampened condition, preferably by stacking them, and permitting them to bleach. Following the attainment of a satisfactory brightness and absorbency by the fibers, they are washed free of bleaching solution and dried by conventional means.

Cotton fibers in any form, and either alone or mixed with other fibers, may be treated by the present method. For example, the fibers may be raw stock, or they may be carded, spun, woven, knitted, felted, or otherwise fabricated into goods.

The fibers are dampened with'the present bleach solution. In damp condition, they contain about 50 to 150 parts by weight of bleach for each parts by weight of fiber. Dampened fibers containing 100 parts by weight of bleach for each 100 parts by weight of fiber are referred to herein as being dampened to the extent of 100 percent. The dampening of the fibers is carried out by conventional means. For example, they may be immersed in the bleach bath, removed from the bath, and squeezed to remove excess bleach. Other suitable means will be apparent to one skilled in fiber-treating.

The bleaching operation is carried out at a temperature at or near room temperature, for example, at about 50 F. to 5., over about 6 to 24 hours. Some heat of reaction is given off in the bleaching operation, and may raise the temperature of the dampened fibers to as much as about 120 F. or even slightly higher. This has been found not to interfere with the bleaching operation.

During the bleaching operation, the fibers normally are kept damp; that is the bleach solution is maintained in the fibers in the amount of about 50% to While the bleach solution may be permitted to evaporate from the fibers to provide somewhat less than 50% saturation during bleaching without destroying the bleachrug efiiciency, the more sensitive cotton fibers may be damaged by the more concentrated alkaline bleach solution which results from excess evaporation, and it therefore is preferred to maintain at least about 50% of bleach liquor in the fibers. The desired degree of dampness may be maintained readily, by merely stacking the fibers to retard evaporation of the bleaching solution. Other means for maintaining the fibers in damp condition may be employed, for example, they may be stored in humid atmosphere, or they may be covered to prevent or retard evaporation. Following the bleaching operation, the fibers are washed free of bleaching solution with water, at room or elevated temperatures.

The bleach solution comprises a typical hydrogen peroxide cold-bleach solution, containing as an added, essential ingredient, about 3 to 15 grams per liter, and preferably about 5 to 7 grams per liter, of a dipersulfate of ammonia or an alkali metal. The aqueous alkaline hydrogen peroxide bleach solution normally will contain, in addition to the dipersulfate, about 0.75 to 5% by weight of hydrogen peroxide, about 5 to 25 grams per liter of sodium hydroxide, or an equivalent amount of another alkalisuchas potassium hydroxide or an alkali phosphate, and a stabilizing amount of a typical bleach bath stabilizer such as sodium silicate or a phosphate. A stabilizing amount of the silicate is about to 50 grams-per liter, and of the phosphate is about 2 to 15 grams per liter. Preferably this solution Will also contain a wetting agent of the type normally used in bleach ing solutions, preferably a non-ionic or anionic wetting agent such as an alkyl aryl sodium sulfonate or an alkyl aryl polyether alcohol, in the amount of about 1 to 5 grams per liter, Hydrogen peroxide and alkali may be place part of the hydrogen peroxide for bleaching, as

well as to improve its effect on the absorbency of the fibers.

It has been found that the bleaching solution containing the dipersulfate should not undergo prolonged heating above about 100 F.before application to the fibers, as such preheating reduces the effectiveness of the dipersulfate in improving the absorbencies and brightnesses of the fibers in bleaching. Heating the dampened fibers containing the bleach to about 120 F. or even higher, however, does not have this deleterious effect.

The following examples are given by way of illustration of the present invention only, and are not intended to limit the scope thereof in any way. For bleaching, comparative bleach liquors in each example were ad justed to the same active oxygen contents by varying the amount of hydrogen peroxide to compensate for active oxygen introduced as dipersulfate.

The brightnesses of the bleached fibers were determined on a Gardner Automatic Multi-Purpose Reflectrometer, manufactured by Gardner Laboratory, Inc., of Bethesda, Maryland. Brightnesses of 80% or better are considered satisfactory.

The absorbencies of the fibers were measured by placing a sample of the cloth in taut condition on a horizontal frame, dropping one drop of distilled water from a height of /8 inch onto the cloth, and measuring the time for disappearance of a specular reflection from the water. Time values of to seconds or less are considered satisfactory.

Fluidities, a measure of the extent of damage to the fibers, were measured by the ASTM Cuprarnmonium Method, D-539-53, with the results being stated as rhes units. Rhes values on the order of about 6 to 7 or lower are considered satisfactory.

The fibers also were tested for ash, for their contents of water-extractable materials, their contents of enzymeextractable materials, and for their contents of fats, oils and waxes, by standard techniques. These additional determinations were made to compare the general properties of fibers c01d-bleached with solutions containing, and those not containing, the dipersulfate. The ash determinations were made by charring samples of cloth in a platinum crucible using a Mekker burner, and mufiling to constant weight. Ash values on the order of 20% to .25% or lower are considered satisfactory. The percent enzyme-extractable values were determined with a solution of Rapidase, a proteolytic enzyme sold by Penetone Co., of Tenafly, New Jersey.

Example 1 Swatches of cotton drill cloth, having a weight of 1.85 yards per pound and a reflectance of 63% was immersed in following solutions A and B, and passed, through rollers to adjust the content of bleach solution on the cloth to 100%. The samples were then packed into, a vessel and covered with a further cloth containing the bleach solution, and permitted to stand for 19 hours at room temperature, about 75 -F. to F. The treated fibers were then washed free of bleach solution by three water washings and dried in an air circulating oven at 200 F. The bleached samples were then tested, with the results reported under the heading Cloth Analysis.

Grams Per Liter Ingredients Solution Solution Hydrogen peroxide 1 18 16; 8 Sodium silicate 2 48 48 Sodium hydroxide. 18 18 Detergent 3 1. 2 1. 2 Potassium dipersulfate 0 7. 2 We fer Balance Balance Hydrogen peroxide used in the various examples was introduced as a 35% by weight solution in water.- The amount reported represents the amount of hydrogen peroxide.

The amount of sodium silicate reported in the various examples is the amount of 42 B. solution employed.

3 The detergent used in the various examples was an alkyl aryl sodium sulionate.

. 1 C O H LYSI 7 Value Sample A Sample B Reflectance, (percent) 81. 83.0 Absorbency- 1 minute 2.5 seconds Fluidity (Rhes) 4. 7 4. 8 Water extractables, (percent)- 0. 48 0. 48 Enzyme extraetables, (percent) 0. 69 0. 61 Fats, oils 6: waxes, (percent) 0.6 0. 28 Ash, (percent) 0. 19 0.21

Example 2 The procedure of Example 1 Was repeated, employing the following bleach solutions:

Grams Per Liter Ingredients Solution Solution Solution A Y B O Hydrogen'peroxide 12. 6 11. 7 11. 7 Sodium silicate 36 36 36 Sodium hydroxide 12 12 12 Detergent 1. 2 1. 2 1. 2 Potassium dipersulfate 0 5. 16 0 Ammonium dipersuli'ate.-. 0 0 5.16 Water Balance Balance Balance CLOTH ANALYSIS Value Sample Sample Sample A B O Reflectance, (percent) 81.6 83.0 83.3 Absorbency Over 1 2.5 sec. 2.0 see.

' nun. Fluidity (Rhes) 4. 7 4. 8 5. 2 Water extractables, (percent) 0.53 0. 48 0. 56 Enzyme extractables, (percent) 0. 53 0.61 0.66 Fats, oils & waxes, (percent) 0. 34 0.28 0.38 ash, (percent) 0. 20 0.20 0.21

Example 3 The procedure of Example 1 was repeated, employing the following bleach solutions:

Grams Per Liter Ingredients Solution Solution Solution A B c 0 Hydrogen peroxide 11. 1 10. 5 10. 5 Sodium silicate 24 24 24 Sodium hydroxide. 12 12 12 Detergent 1.2 1.2 1 2 Potassium dipersuliate. 0 5. l 0 Sodiumdi'persulfate 0 0 5. 1

CLOTH ANALYSIS Sample Sample Sample Value A B C Reflectance (percent) 80.1 82.8 82.6 Absorbency Over 2 sec. 13 sec.

mm. Water extractables (percent) 0.51 0.55 not demined. Enzyme extractables (percent) 0. 49 0.60 Do. Fats, oils 8: waxes (percent) 0.53 O. 46 Do. Ash (percent) 0.17 0.19 Do.

Swatches of the cloths treated with solutions A and B were washed and tested after being stored for 6 hours. The swatches treated with solution A had a reflectance of 79.9% absorbencies of over 3 minutes. The swatches treated with solution B had reflectances of 82.0%, and absorbencies of only seconds.

Example 4 In this example, the cloth treated was an 80 x 80 thread cotton print cloth, having a weight of 4 yards per pound.

As shown in the above examples, cotton fibers bleached with the present dipersulfate-containing cold-bleach solutions have better brightnesses, and much better absorbencies, than similar fibers treated with typical cold-bleach solutions not containing a dipersulfate. These improvements are achieved with no increase in the active oxygen content of the bleaching bath, and with no substantial change in other properties of the bleached cloth. These improved bleaching results make the cold-bleaching method suitable for bleaching cotton fiber products which must have high absorbencies, and thereby bring the economic advantages of the cold-bleach process into this area of fiber bleaching.

While the principle of this invention has been explained and exemplified in a manner so that it can be readily practiced by those skilled in the art it will be understood that various modifications and changes may be made and hence the invention is not to be limited to the above example or disclosure except as set forth in the appended claims.

We claim:

1. In the method of cold bleaching cotton fibers by dampening the fibers with a bleach comprising an aqueous alkaline hydrogen peroxide solution and permitting them to stand in a dampened condition at temperatures of about 50 F. to about F., and wherein the absorbency of said cotton fibers is ordinarily diminished by this treatment, the improvement which comprises employing as the bleaching bath an aqueous alkaline hydrogen peroxide solution containing as an essential ingredient, a dipersulfate from the group consisting of the alkali metal dipersulfates and ammonium dipersulfate, whereby the absorbency of said cotton fibers is not materially diminished.

2. Method of claim 1 in which the fibers in dampened condition contain about 50 to parts by weight of bleach for each 100 parts by weight of fiber.

3. Method of claim 2 in which the bleach comprises about 0.75% to 5% by weight of hydrogen peroxide, about 3 to 15 grams per liter of a dipersulfate from the group consisting of the alkali metal dipersulfates and ammonium dipersulfate, an amount of alkali equivalent to about 5 to 25 grams per liter of sodium hydroxide, and a stabilizing amount of a stabilizer.

4. Method of claim 3 in which the dipersulfate is potassium dipersulfate.

5. Method of claim 3 in which the dipersulfate is sodium dipersulfate.

6. Method of claim 3 in which the dipersulfate is ammonium dipersulfate.

References Cited in the file of this patent UNITED STATES PATENTS 1,894,277 Manahan Jan. 17, 1933 2,110,649 Franz Mar. 8, 1933 2,882,121 Fell Apr. 14, 1959 2,901,319 D'Addieco Aug. 25, 1959 OTHER REFERENCES Price: Per-Acids and Their Salts, published by Longmans, Green & Co., London, 1912, pages 38 and 52.

Ser. No. 197,895, Franz (A.P.C.), published June 15, 1943.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,026,166 March 20, 1962 Gerald Thomas Gallagher et al.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 40, for "special" read specialty column 3, lines 40 and 41, for "Reflectrom eter" read Reflectometer line 64, for "Mekker" read Meker column 4, Example 3, in the table, column 1, line 6 thereof, for "Sodiumdipersulfate" read Sodium dipersulfate column 5, Example 3, in the table, column 4, lines 3 and 4,thereof, for "not demined" read not determined line 16, for "79.9% absorbencies" read 79.9% and absorbencies Signed and sealed this 24th day of July 1962.

SEAL) LtleSt:

\RNEST W. SWIDER I DAVID L. LADD .ttesting Officer Commissioner of Patents 

1. IN THE METHOF OF COLD BLEACHING COTTON FIBERS BY DAMPENING THE FIBERS WITH A BLEACH COMPRISING AN AQUEOUS ALKALINE HYDROGEN PEROXIDE SOLUTION AND PERMITTING THEM TO STAND IN A DAMPENED CONDITION AT TEMPERATURES OF ABOUT 50*F. TO ABOUT 120*F., AND WHEREIN THE ABSORBENCY OF SAID COTTON FIBERS IS ORDINARILY DIMINISHED BY THIS TREATMENT, THE IMPROVEMENT WHICH COMPRISES EMPLOYING AS THE BLEACHING BATH AS AQUEOUS ALKALINE HYDROGEN PEROXIDE SOLUTION CONTAINING AS AN ESSENTAIL INGREDIENT, A DIPERSULFATE FROM THE GROUP CONSISTING OF THE ALKALI METAL DIPERSULFATES AND AMMONIUM DIPERSULFATE, WHEREBY THE ABSORBENCY OF SAID COTTON FIBERS IS NOT MATERIALLY DIMINISHED. 